feat: implement AsFd/AsHandle to mirror the AsRaw* variants (#230)

We don't implement the "into" variants as that'll drop and delete the
temporary file.

Cargo.toml

@@ -36,5 +36,8 @@ redox_syscall = "0.3"
 [dev-dependencies]
 doc-comment = "0.3"
 
+[build-dependencies]
+autocfg = "1"
+
 [features]
 nightly = []

build.rs

@@ -0,0 +1,10 @@
+fn main() {
+    let ac = autocfg::new();
+
+    #[cfg(unix)]
+    ac.emit_trait_cfg("std::os::fd::AsFd", "fd");
+    #[cfg(windows)]
+    ac.emit_trait_cfg("std::os::windows::io::AsHandle", "fd");
+
+    autocfg::rerun_path("build.rs");
+}

src/file/mod.rs

@@ -1034,6 +1034,13 @@ impl Seek for &NamedTempFile<File> {
     }
 }
 
+#[cfg(all(fd, unix))]
+impl<F: std::os::unix::io::AsFd> std::os::unix::io::AsFd for NamedTempFile<F> {
+    fn as_fd(&self) -> std::os::unix::io::BorrowedFd<'_> {
+        self.as_file().as_fd()
+    }
+}
+
 #[cfg(unix)]
 impl<F> std::os::unix::io::AsRawFd for NamedTempFile<F>
 where
@@ -1045,6 +1052,17 @@ where
     }
 }
 
+#[cfg(all(fd, windows))]
+impl<F> std::os::windows::io::AsHandle for NamedTempFile<F>
+where
+    F: std::os::windows::io::AsHandle,
+{
+    #[inline]
+    fn as_handle(&self) -> std::os::windows::io::BorrowedHandle<'_> {
+        self.as_file().as_handle()
+    }
+}
+
 #[cfg(windows)]
 impl<F> std::os::windows::io::AsRawHandle for NamedTempFile<F>
 where